Full-waveform sonic (FWS) devices can be used in wellbores to collect FWS data which can be processed to provide information about lithologic and fluid properties of a formation. Different from other geophysical measurements such as seismic and vertical seismic profile (VSP), FWS data is typically measured using a small sampling time interval, but a large offset spacing, thus contributing to an aliasing effect in the FWS data. Existing FWS processing methods overlook the aliasing effect and simply apply processing technologies that are developed in other fields to FWS data, causing uncertainty and inaccuracy in FWS wavefield separation results.